# Example 1: corr_pH - simple temperature correction of pH

Consider an RBR*concerto³* C.T.D.pH logger. Without temperature correction, the pH output from Channel-4 would be a simple linear function of the raw data:

where R is the normalized voltage ratio from Channel-4 monitoring the pH sensor, **c0**,** c1** are the core coefficients of the linear equation, and **pHraw** is the uncorrected output in pH units.

The parameter pH is well known to have a dependence on temperature, so a more accurate value is obtained if the compensated version of the equation is used. This is typically expressed in a form such as:

Casting this into the form used by the logger, corr_ph, is simple:

where

**pHraw**is c0 + c1 * R as before, now an intermediate variable in the equation,**x0**corresponds directly in value to the constant "Kph",**x1**is the calibration pH "pHcal", generally 7.0,**x2**is the calibration temperature 'Tcal' in °C,**n0**is the index of the temperature channel (2 in this example),**value(n0)**is the final output value of the temperature channel in °C,**pHcorr**is the corrected output in pH units.

Note that this equation is for the output from Channel-4, so the source of the primary raw data R is implicitly Channel-4: there is no **n** index to specify where the raw data originates.

## Examples

```
>> calibration 4 type
<< calibration 4 type = ph__02
```

Confirm the channel type.

`>> calibration 4 datetime = 20171201000000, c0 = 15.23461, c1 = -0.198743`

Set the core coefficients.

`>> calibration 4 datetime = 20171201000000, x0 = -0.00302, x1 = 7, x2 = 24.943`

Set the cross-channel correction coefficients.

```
>> calibration 4
<< calibration 4 type = ph__02, datetime = 20171201000000, c0 = 15.23461, c1 = -0.198743, x0 = -0.00302, x1 = 7, x2 = 24.943, n0 = 2
```

Request confirmation of all calibration coefficients.